In recent years, there has been advancement in small-size portable electronic devices such as cellular phones and hearing aids. Besides, devices that operate in contact with human body have been increasingly commercially available. For example, biological information measuring devices that acquire biological information such as body temperature, blood pressure, and pulse, and automatically transmit the acquired information to a facility such as a hospital have been developed. For another example, body-attached devices that, upon application of a potential to the skin of human body, supply medicine etc. through the skin into the body have been developed.
Under these circumstances, the batteries for supplying electric power to the above-mentioned small-size electronic devices are required to be thinner and more flexible. Thin batteries that have been already developed include paper batteries, thin flat batteries and plate-like batteries. In these batteries, the strength of the housing is high, but it is difficult to make the battery more flexible and further thinner.
In order to make the thin batteries more flexible and further thinner, a technique of using a thin and flexible laminated film as the housing has been proposed (see, e.g., Patent Literatures 1 and 2). Specifically, as shown in FIG. 9, a thin battery includes an electrode group 101 and a housing 102. The electrode group 101 is formed by stacking flat plate-like positive electrode and negative electrode with a separator interposed therebetween. A positive electrode lead 103 and a negative electrode lead 104 are electrically connected to the positive electrode and the negative electrode, respectively. The housing 102 is made of a laminated film, and serves to cover the positive and negative electrodes, while allowing the end portions of the positive and negative electrode leads to be exposed outside the housing. The exposed end portions are used as positive and negative electrode terminals.
Another possible technique for making thin batteries more flexible and further thinner is to reduce the thickness of the electrode group. For example, one proposal suggests forming an active material layer of the positive or negative electrode by a vapor phase process, thereby to reduce the thickness of the active material layer (see, e.g., Patent Literature 3).